Podrías escribir WITH consulta
por esto:
WITH month_amount AS
(
SELECT
sum(amount) AS amount,
date_trunc('month', date) AS month
FROM Amount
WHERE user_id = 55 -- AND ...
GROUP BY month
)
SELECT month, amount
FROM
(SELECT generate_series(min(month), max(month), '1 month') AS month
FROM month_amount) x
LEFT JOIN month_amount
USING (month)
ORDER BY month;
Resultado de ejemplo:
SELECT * FROM amount WHERE user_id = 55;
amount_id | user_id | amount | date
-----------+---------+--------+------------
3 | 55 | 7 | 2011-03-16
4 | 55 | 5 | 2011-03-22
5 | 55 | 2 | 2011-05-07
6 | 55 | 18 | 2011-05-27
7 | 55 | 4 | 2011-06-14
(5 rows)
WITH month_amount ..
month | amount
------------------------+--------
2011-03-01 00:00:00+01 | 12
2011-04-01 00:00:00+02 |
2011-05-01 00:00:00+02 | 20
2011-06-01 00:00:00+02 | 4
(4 rows)
